1. Field of the Invention
This invention relates to a speed-change power transmission, and more particularly to a stepless speed-change power transmission for a vehicle.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional speed-change power transmission disclosed in Taiwanese Invention Patent Publication No. I308613 includes a crankshaft box 12, a crankshaft 13 disposed in the crankshaft box 12, an outer cover 14 cooperating with the crankshaft box 12 to define an accommodating space 100 therebetween, a belt type speed-change system 15 disposed in the accommodating space 100 and driven by the crankshaft 13, and an air-guiding shield 16.
The crankshaft box 12 has an intake port 121 and an exhaust port 122 that, are in fluid communication with the accommodating space 100. The belt type speed-change system 15 includes a driving pulley 151, a driven pulley (not shown), and a transmission belt 154 trained on the driving pulley 151 and the driven pulley. The air-guiding shield 16 has a C-shaped flange 161 disposed around the driving pulley 151 and formed with an opening 162 that is opened toward the exhaust port 122. The driving pulley 151 includes a fixed pulley half 152 and a movable pulley half 153. The flange 161 is disposed around the fixed pulley half 152.
Due to the guiding action of the flange 161, air flows from the intake port 121 onto the fixed pulley half 152. Rotation of the fixed pulley half 152 results in flow of the air from the fixed pulley half 152 into the accommodating space 100 via the opening 162. Finally, the air is discharged through the exhaust port 122 to dissipate heat from the belt type speed-change system 15.
Since the flange 161 is formed with only one opening 162 that is opened toward the exhaust port 122, a majority of air is urged directly toward the exhaust port 122 by the fixed pulley half 152, and cannot impart a sufficient cooling effect to the movable pulley half 153.